Basing oven



Nov.'l2, 1957 L. HARRls 2,812,933

' BASING ovEN Filed May 2, 1955 MMS' u?? 1"u vYIIIIIgI.

. INVIENTOR. I Enuann- Haat-'ns United States Patent O BASING OVEN Leonard Harris, West Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 2, 1955, Serial No. 505,194

4 Claims. (Cl. 263-2) This invention relates to ovens and particularly to improvements in so-called basing ovens for heat-sealing an insulating base to the terminal end of the glass envelope of an electron tube.

In cementing a base constituted, for example, of a thermosetting resin to the glass envelope of an electron tube, economy and certain electrical considerations may dictate the use of a thermally sensitive cement having a curing point which approaches that of the blistering temperature of the material of which the base is comprised. Thus, if the base material comprises a phenolic resin containing an insulating filler, the base may blister (and hence be rendered defective) if subjected to a temperature of, say 175, and the phenolic cement may have to be exposed to a temperature of at least 155 C. for a period of at least one minute during the bonding operation. In basing machines wherein the cement receives its heat by conduction thru the tube base localized overheating and consequent blistering of the base material may occur adjacent to the area or areas where the heating elements are located.

Accordingly, an object of the present invention is to provide an improved basing oven and one which by reason of its uniform heat distribution shall permit the use of a quick curing basing cement having a curing point which approaches that of the blistering temperature of the base.

Stated generally, the foregoing and related objects are achieved in accordance with the invention in a basing oven having a plurality of heat-compartments which cornmunicate with the ambient, directly or indirectly, adjacent to the areas at which the heat is applied, whereby the resulting convection currents set-up in said compartments prevent localized overheating of the tube base and consequent blistering of those areas of the base which lie in register with the heat applicators.

The invention is described in greater detail in connection with the accompanying single sheet of drawings, wherein:

Fig. 1 is a view in perspective of a basing oven constructed in accordance with the invention and showing an electron tube assembly arranged in a position to be er1- tered into the oven; and

Fig. 2 is a sectional view taken through line 2-2 of Fig. l with the parts of the tube-assembly which are to be bonded together shown positioned within the oven.

In the embodiment of the invention that has been selected for illustration the oven comprises a short openended vertically extending cylinder 1 upon one end of which the insulating base 3 on one end 5 of the tube 'I is seated as by a plunger 9 with the prongs 11 of the base within the bore of the cylinder. The cylinder or socket 1 is contained within two heating compartments 13 and 15 the walls of which are defined by two U-shaped metal plates or baies 17 and 19 of different dimensions, arranged with the arms of the smaller U 17 presented across an intervening space to the interior of the larger one 19. The larger U 19 is consequently open ended adjacent to nozzles 27 and 27 to be described. The large U 19 is shown broken at the center of the U. The top of the inner compartment 13 has a cover plate 21 which is shown secured, as by screws 23, to a flange 25 on the cylinder 1 upon which the tube-base 3 is seated. The inner and outer compartments 13 and 15 are heated by radiation from their U-shaped metal walls 17 and 19 which receive their heatfrom gas ilames emanating from nozzles 27, 27', and 29, 29', respectively, which are directed upon the outer surface ofthe curved portion of each U. Where, as in the instant case, the oven is arranged to be supported (as indicated at 31) on an extension 21 of the topplate 21, the gas jets 27, 27 may be directed upon the smaller (inner) U 17 thru holes 33 and 33 provided for the purpose, in said extension.

In the oven as thus far described localized overheating of the tube-base 3 may occur at the small areas on the base which lie in register with the parts of the walls 17 and 19 Aupon which the gas ilames from the nozzles 27, 27', 29, 29', impinge. Such localized overheating would be more pronounced at the rear of the oven that at the front because the open end of the inner compartment 13 communicates with the outer compartment 15, and with the ambient, near the front of the oven (see Fig. 2). As a consequence convection currents are set-up at the front of the outer compartment and serve to distribute the heat more evenly over the front part of the surface of the base 3 than could be achieved by radiation alone.

lnA order to set-up convection currents for dissipating the hot gas entrapped (by the cover-plate 21) within the cylindrical socket 1 and at the rear of the compartments 13 land 15, and thus to prevent localized overheating of the parts of the tube-base which lie in register with the rear jets 27 and 27', the socket 1 is provided at its rear with an arcuate cut-away portion or vent 35 which communicates with the inner compartment 13, and the coverplate 21 is cut away to provide an opening 37 to the ambient adjacent to that region of the compartment 13 which is subjected to the direct heat of the rear jets 27 and 27'. Thus, by locating the heat applicators 27, 27', 29, 29 adjacent to the surface areas of the U-shaped baffles along which the convection currents pass to the ambient, localized overheating which would result in blistering of the areas of the tube-base which lie in register with said applicators, is prevented.

What is claimed is:

l. An oven for heat-sealing an assembly comprising a pronged base, a glass envelope and an interposed serving of a thermally sensitive cement; said oven comprising; a vertically extending cylinder having an upper end, an aperture in its wall adjacent to said end, and a lower openend against which the bottom of said base is adapted to bear when the prongs thereon are entered in the bore of said cylinder; two U-shaped metal bailles of different dimensions disposed in spaced relationship about and parallel to the outer surface of said cylinder with the arms of the smaller U presented across an intervening space to the interior of the larger U to define the boundaries of two heat chambers which communicate with each other and with the ambient adjacent to the open end of the smaller U whereby to permit the flow of convection currents therethrough when said oven is heated; a cover-plate spanning said inner chamber adjacent to the closed end of said inner U, said cover-plate having an opening therein adjacent to said cylinder-aperture to permit the flow of convection currents between the cylinder, the closed end of said inner chamber, and the ambient surrounding the aperture in said cover plate; and a plurality of applicators for applying heat to the outer surface of each of said U-shaped metal bafes,tsaid heat applicators being located adjacent to the parts of said bales along which said convection currents pass to the ambient, whereby to minimize localized overheating of the areas of said tube-base which lie in register with said heat applicators.

2. Heating apparatus comprising a support, a U-shaped first heatable member fixed to one side of said support and havinga pair ofheat receiving portions adaptedto be heated by flames, a second heatable member disposedlad-` jacent tothe opening between the legs of said U-shaped first heatable member and havingT a pair of heat receiving portions adapted tobe heated by ames, whereby said heatable members provide a baiTled heat retaining system,

a workpiece receiving cylinder xed to said support and' within said U-shaped member and adapted to hold a workpiece on said side of said support and spaced from said heatable members, whereby said heatable members and the workpiece held within saidcylinder dene between them a space for utilizing convection currents of heated gases to transfer heat from saidheatable member to said workpiece, saidY support having a vent therethrough at the portion thereof adjacent to said pairs of heat receiving portions of vsaid iirst heatable member for providing a communication between said space and the side of` said support remote from said one side thereof, whereby said vent utilizes convection-currents to draw off hot gases at saidV heat receiving portions of said first heatable member, said cylinder having an arcuate slot at a portion thereof adjacent to said vent thereby eX- posing the portion of a workpiece adjacent to said slot to a flow of gases toward said vent for preventing localized overheating of said workpiece.

3. A basing oven for heat-sealing an assembly comprising a glass-tube and an insulating base for said tube, with the aid of an interposed serving of a thermally responsive cement; said oven comprising, a socket for receiving the parts of the assembly to be sealed, a plurality of metal batiles disposed in spaced apart relationship about said socket to provide a plurality of heat-chambers therebetween, aplurality of heat-applicators for applying heat directly to the outer surface of each baile at spaced apart regions about the space to be occupied by said tubebase, and means adjacent to said spaced apart regions communicating with the spaces between said socket and the parts of said bales to which the heat is applied for venting said heat-chambers.

4. An oven comprising a support having a cylinder adapted to receive a workpiece and a pair of U-shaped heatable members partially overlapping each other and surrounding said cylinder, each of said heatable members having heat receiving portions adjacent to the legs of the U of the other member and adapted to be heated by ames, said support and said cylinder each having in registry with the other at least one aperture disposed adjacent to said'heat receiving portions of one of said members and between thelegs of the U of the other member for utilizing convection currents to draw ofi hot gases at said heat receiving portions thereby preventing localized overheating within said oven.

References Citedin the tile of this patent UNITED STATES PATENTS 1,617,955 Kutchka Feb. l5, 1927 1,997,694 Morick etal Apr. 16, 1935 2,069,386 Paluckij Feb. 2, 1937 2,650,420. True 1 Sept. l, 1953 

